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derive: reject unions as they require unsafe code #231

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GuillaumeGomez merged 2 commits intoaskama-rs:masterfrom
Kijewski:pr-no-unions
Nov 11, 2024
Merged

derive: reject unions as they require unsafe code #231
GuillaumeGomez merged 2 commits intoaskama-rs:masterfrom
Kijewski:pr-no-unions

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@Kijewski Kijewski commented Nov 10, 2024

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github-advanced-security[bot]
github-advanced-security bot found potential problems Nov 10, 2024
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rinja_derive/src/input.rs

impl TemplateArgs {
pub(crate) fn new(ast: &syn::DeriveInput) -> Result<Self, CompileError> {
// FIXME: implement once <https://github.com/rust-lang/rfcs/pull/3715> is stable

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A "TODO" or similar was left in source code, possibly indicating incomplete functionality

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@GuillaumeGomez
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GuillaumeGomez commented Nov 11, 2024

I'm not sure how difficult it would be to support union. Apart from adding unsafe when accessing its fields, is there anything else?

In the meantime, merging this. Thanks!

@GuillaumeGomez GuillaumeGomez merged commit d00e638 into askama-rs:master Nov 11, 2024
@Kijewski Kijewski deleted the pr-no-unions branch November 11, 2024 10:30
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Kijewski commented Nov 11, 2024

Adding unsafe would be all that is needed, AFAICT. I don't actually see a use case for this feature, though, so implementing it would be far down on my to do list. We cannot simply add this feature in a safe context, because accessing union members may allow accessing uninitialized memory, which can be bad.

Actually, looking at the RFC again, I am not sure if it would be useful to us. A proc_macro does not see the #[unsafe(derive(Template))] part of #[unsafe(derive(Template))] struct X, and we would have to add e.g. a #[unsafe(derive(UnionTemplate))]. Maybe I'll think about this further and comment in rust-lang/rfcs#3715.

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GuillaumeGomez commented Nov 11, 2024

Sounds good to me. Not high priority for me either.

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